1. Technical Field
The present invention relates generally to an automotive antenna unit and more particularly, to an automotive antenna unit located on the underside of a vehicle body.
2. Background Art
Various types of antenna units for vehicles have been proposed. For example, a bar-type antenna units for use in automotive vehicular radio systems are well known in the art. Such antenna units however require housing space and must be positioned so as to be extendable without obstruction. Consequently, a small sensitive antenna element which may be installed at a non-visible position on a vehicle has been sought.
Such antenna units are generally disposed on a floor panel of a vehicle. An antenna unit typically includes an earth conductive plate fixed on the floor panel, a radiating conductive plate spaced- from the earth conductive plate by a given distance, and a feed pin, and a supporting pin each connecting between both conductive plates. In such an antenna unit, the radiating conductive plate projects downward from the bottom of the vehicle and it is a thin flat metal member, which is suspended by only the feed and the supporting pins. Thus, the mechanical rigidity of the radiating plate is relatively weak and therefore tends to receive shocks due to stones or mud on road surfaces. In the event an impact of stones or mud, breaking of the pins or disconnection between the conductive plates and the pins tends to occur. Additionally, in antenna elements of the prior art, adjustments of the distance between the radiating conductive plate and the earth conductive plate or of the particular geometry of the radiating conductive plate, according to the type of vehicle, are necessary in order to adjust resonance at the operating frequency of the antenna unit. Accordingly, a new conveniently adjustable type of antenna element with excellent durability under road conditions in different types of vehicles has long been sought by designers.